David Addison Haig's early education was at a bush school. However, he earned a free place at the University of Sydney, which he took up in 1952, where he studied economics and worked for a Graduate Diploma in Education. He joined the Sydney University Regiment, receiving a commission as lieutenant in 1956.
Graduating with a Bachelor of Economics in 1957, he commenced a career in high-school teaching, but then turned his attention to a career in commerce, where the highlights included becoming chairman of directors of a public company, founding a building society that became one of Australia's minor banks, and negotiating a successful takeover, all before the age of thirty.